This is a study of the question of whether moral principles, as justified by a contractualist scheme, such as Scanlon's, are binding on persons, i.e., give them reasons to act in accordance with such principles. I argue that for those agents who meet the motivational conditions that Scanlon lays down, i.e., those who seek to reach agreement with others on principles that are not rejectable, such principles are binding. But on those who do not meet the motivational condition the principles are not binding